The Thar is a small river of France, in the administrative region Basse-Normandie, département de la Manche

Manche

Manche is a French department in Normandy named after La Manche , which is the French name for the English Channel.- History :Manche is one of the original 83 departments created during the French Revolution on March 4, 1790...

. It is only 25 km (16 mi) long, rising to the east of La Haye-Pesnel and emptying into the Bay of Mont Saint-Michel

Mont Saint-Michel

Mont Saint-Michel is a rocky tidal island and a commune in Normandy, France. It is located approximately one kilometre off the country's north-western coast, at the mouth of the Couesnon River near Avranches...

, in the English Channel

English Channel

The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...

.

In the Middle Ages the Thar formed the traditional boundary between the Cotentin to the north and the Avranchin

Avranchin

The Avranchin is an area in Normandy, France, corresponding to the territory of the Abrincates, tribe of Celts who also gave their name to the city of Avranches, main town of the Avranchin....

to the south.